As the related art of a field of present technology, for example, JP 2008-197575 A (Patent Literature 1) is known. In Patent Literature 1, “positions of standard marks M1 to M4 included in image data imaged by an optical sensor 26 are specified and a boundary position of reproduction signal light RS and reproduction reference light RR is specified from the positions. If the boundary position can be specified, a target imaging diameter Dt is calculated on the basis of the boundary position. In addition, an actuator AC1 for iris adjustment is driven by a driver 30c, such that a diameter of an aperture portion AP becomes the target imaging diameter Dt at the time of being imaged by the optical sensor 26.” is described. In addition, in Patent Literature 1, “a position of a light shielding plate 20 can be adjusted in a plane orthogonal to an optical axis direction by driving an actuator AC2 for position adjustment and a position of the aperture portion AP can be adjusted in a height direction (Y) and a width direction (X).” is described.